Electrolytic deposition of charged dyes for photoconductographic processes



Aprl] 19, 1966 EL 3,247,081

ELECTROLYTIC DEPOSITION OF CHARGED DYES FOR PHOTOCONDUGTOGRAPHIC PROCESSES Filed Aug. 7, 1964 l PROCESSED Pmme/aqPH/c I l IMAGE m PHOTOCONDUCT/VE CONDUCT/V5 SUPPORT FigJI Figllz RaymondEReiihel IN VEN TOR.

United States Patent ELECTROLYTHC DEPOSITION 0F CHARGED DYES FOR PHOTtNZONDUCTOGRAPI-HC PROCESSES Raymond F. Reithel, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey Filed Aug. 7, 1964, Ser. No. 389,514 Claims. (Cl. 20418) This is a continuation-in-part application of Reithel U.S. Serial No. 858,903, filed December 11, 1959, and abandoned on September 19, 1964.

This invention relates to electrolytic recording and more particularly to electrolytic recording for photoconductography.

Photoconductography is described in detail in British Patent 188,030, Von Bronk, and British Patent 464,112, Goldmann. British Patent 789,309, Berchtold, describes an improvement in the process using a protective layer between photoconductor and recording layer and Belgian Patent 561,403, describes, in considerable detail, systems using zinc oxide as the photoconductor. This latter patent, and also German Patent 151,971, Kalisher et al. describe formation of the image after rather than during exposure of the photoconductor.

Photoconductographic materials consist essentially of a support bearing an electrically conductive carrier on which is coated a layer of photoconductive material. The type most widely used at the present time consists of a metalized support as the conductive carrier and a finely powdered photoconductive zinc oxide dispersed in a resinous binder as the photoconductive layer. Other metallic oxides or sulfides may be used in place of zinc oxide in the photoconductive layer.

It is known that zinc oxide photoconductors can be made panchromatically sensitive. S. N. Thompson, 2,727,807 and 2,727,808, both issued December 20, 1955, for example, describe techniques for doing this.

The sensitized photoconductive layer of photoconductographic material becomes electrically conductive in the specific areas where it has been exposed to light of wavelengths to which it is sensitive.

In Belgian Patent 561,403, Johnson et al form dye images by using in their development process an electrolyte containing diazonium salts plus coupler material in acid medium. During the electrolytic process, the diazonium salt couples with the coupler to form a dye image on the photoconductive surface. In another process they use a mixture of a diazotizable amine, coupler material and an electrolyte containing sodium nitrite. During electrolysis, the diazonium compound is formed on the exposed areas of Zinc oxide which subsequently couples with the coupling materials to produce the dye image. In another process dye images are formed by using zinc oxide coatings that are strongly colored by suitable oxidizable or reducible dyes which are altered at light exposed areas by electrolysis in aqueous bleach solutions.

It is also known that charged colloidal particles of Prussian blue suspended in Water may be used to form a Prussian blue image on the photoconductor surface of the photoconductographic material when it is simultaneously exposed and developed by electrolysis. Intense exposure of the photoconductor surface in absence of colloidal suspension makes possible subsequent development of a faint image in the presence of the suspension.

It is one object of my invention to provide a novel electrolytic process for the development of intense dye images on photoconductographic material after they have been exposed to imagewise actinic radiation.

Another object of my invention is to provide a novel means for developing dye images on photoconductographic materials by an electrolytic process in which a simple, stable dye solution is used as an electrolyte and developer.

Another object is to provide a simple electrolytic process for producing on an exposed photoconductographic material a strong dye image less subject to fading from exposure to heat and light than are the dye images produced by many of the prior art processes.

Still another object is to provide a simple, electrolytic process for developing colored images on exposed photoconductographic materials which do not have incorporated image forming bleachable dyes or image forming dye precursors in the sensitive element, so that the color of the image produced can be determined at the time of processing merely by selecting a solution containing the appropriately colored dye.

Still another object is to provide a multitude of different dye solutions which can be used in my electrolytic process for producing a variety of different colored images.

Other objects will become apparent from the specification.

These objects are accomplished by use of the novel process of my invention. According to my invention, a light-sensitive photoconductographic material is developed either during or after a suitable light exposure to an image, by applying, to the photoconductive surface of the exposed material, a film of an aqueous solution contain ing colored, electrically charged dye ions, and then electrolytically depositing these colored dye ions in an imagewise manner on the areas of the photoconductive layer that were exposed to light. The remaining solution containing undeposited dye ions is then removed from the photonconductive surface leaving the dye image on a background consisting of the photoconductive layer in its original color.

My process can be used to produce dye images of the desired color on any of the photoconductographic materials that do not contain incorporated dyes or dye precursors that upon development produce a dye image. It is to be understood, however, that the photoconductographic materials used in my process may contain sensitizing dyes or other sensitizing materials in the photoconductive layer. The photoconductographic material may have any of the supports such as paper, cellulose esters, glass, ceramics and others, provided they are ren dered suitably conductive, such as with a metal foil laminate. Any of the various types of photoconductors can be used in the photoconductive layer, such as the oxides and sulfides of zinc, bismuth, antimony, lead cadmium, tellurium and others.

Non-rectifying photoconductors (when in contact with an electrolyte) are used for anodic deposition, including cadmium sulfide, cadmium selenide, cadmium telluride, etc.

The dyes used to produce images by my process are characterized by being water-soluble or Water-alcohol soluble and having, when in solution, a net electrical charge on the dye ion. Although dyes having either negatively or positively charged dye ions may be used, I have found that it is preferable to use dyes which have a positively charged dye ion and are thus adapted to cathodic deposition, since current flow between an electrolyte and some of the known photoconductive materials takes place best when the conductive support of the photoconductographic material is negative with respect to the externally applied electrode used during the electrolytic process. Dyes having negatively charged dye ions will be just as valuable in my process as those having positive charges with photoconductographic systems that deposit the dye on the counterelectrode rather than on the photoconductor or with systems that either do not have this rectifying effect on the passage of an electric current or which conduct electricity in the direction opposite to that of the well-known photoconductors, especially zinc oxide.

Although there are a number of classes of dyes which have charged dye ions useful in my process, the preferred dyes having positively charged dye ions can be illustrated by those produced from the chromogens:

(I) Triphenyl methane chromogen o c1- Q (11) Oxazine chromogen (III) Thiazine chromogen intended to limit the dyes of this type which are useful in the invention.

Dye Identification in 7th Edition of Farbstofitabellen by Schultz Dye and Lehmann Name No.

Malachitgriin 754 Anilinblau. 792 Fuchsin. 780 Setoglucine O Seteglaucin O 755 Oxaziue dyes:

Galloeyauine Gallocyanin 998 Cotton blue BB. Baumwellblau BB 1026 I'leldolas blne 1025 Capri blue GON 991 Nile blue 1029 Nitroso blue MR.- Nitrosoblau MR .1 1023 Thiaziue:

Methylene blue Mehtylonblau 1038 Methylene green l\iethylengriin 10 Lauths violet Lauths Violett; 1036 Toiuidin blue. '1oluidinblau O 1041 'Ilrionine blue... Thieninblau 1042 A Brilliant Alizarin blu Brillantalizarinblau 3 1048 zine:

Neutral red N eutralrot 946 The color of the dyes, their chemical structure, and the method of preparing them may be found in Farbstofftabellen by Schultz and Lehmann, 7th edition.

Illustrative examples of water-soluble negatively charged dye ions (acid dyes) that are useful for anodic deposition according to my invention include known dyes, such as, Benzo Fast Yellow SGL, a bisazocarboxylate dye (CI. 346); Chicago Blue 6B, a bisazosulfonate dye (Cl. 518); Benzo Fast Red 8BL, a bisazosulfonate dye (Cl. 278); Diamine Violet N, a bisazodisulfonate dye (Cl. 394); etc. These and other water-soluble negatively charged dyes are used to advantage in my process for anodic deposition on photoconductors useful in anodic deposition, such as, cadmium sulfide, cadmium selenide, cadmium telluride, etc.

Most of the dyes used in my process are water soluble and can be dissolved in the concentrations used in my process without any diificulty. For some dyes, however, it may be necessary to use alcohols such as methyl alcohol or ethyl alcohol to wet and dissolve the solid dye particles, and water then can be added to form the solution used in my process. Although the dyes may be used at various concentrations in water, they are normally used in the preferred range of /2 to 2% by weight.

The dye solution used for my process may contain besides the dye and water, small amounts of suitable solubilizing compounds, or even larger amounts of weakly ionized compounds, or in some cases, small amounts of polar compounds, such as, gelatin or gum. Polar compounds, however, tend to decrease the efficiency of dye deposition and their use should be avoided.

The electrolytic deposition of the dye ions can be accomplished by applying a potential difference of from about 5 volts to about 150 volts between the conductive carrier and an electrode which is brought into contact with the dye solution that has been placed over the photoconductive layer. A preferred range of potential dif ferences is from about 20 volts to about volts. The electrode may be in the form of a metal plate which covers the photoconductive layer so that the electrolysis is conducted simultaneously in all areas of the picture or the electrode may be applied in the form of a conducting roller or a conducting viscose sponge brush electrode that is moved progressively over small areas of the photoconductive surface until the surface is completely and uniformly electrolyzed.

My invention is illustrated by the accompanying drawmgs.

In FIGURE 1, light from light source 11 is passed through the processed photographic image 12 to expose the light sensitive photoconductive layer 13 that is coated on the conductive layer 14 which is on the support 15.

In FIGURE II, the light exposed image in the left-hand portion of layer 13 has been developed electrolytically by the passage of a direct current through the dye solution electrolyte film 17 applied by the viscose sponge 16 and between sponge 16 which serves as the anode and the light exposed conducting areas of the photoconductive layer which are made the cathode.

In FIGURE III, the light exposed image in the lefthand portion of layer 13 has been developed by another method in which a direct current is passed through the dye solution electrolyte film 17 applied by the conductive roller 18 and between roller 18 which serves as the anode and the light exposed conducting areas of the photoconductive layer which are made the cathode.

Alternatively the dye solution film 17 may be applied to the exposed photoconductive surface by means other than the conductive sponge 16 or the conductive roller 18 of FIGURE 11 and FIGURE 111 respectively and then the dye image is developed electrolytically by passing the anodic sponge 16 or anodic roller 18 over the dye solution wetted photoconductive surface.

FIGURE IV shows the completely developed image on layer 13 made by either the process illustrated by FIGURE II or FIGURE III.

The junction between an electrolyte and the metallic oxides or sulfides used in known photoconductive layers has, as has been described, what appears to be a rectifying effect on the passage of electric current. Because of this, it is possible to use either a source of alternating or direct current for my electrolytic process. Direct current, however, is usually used in such a way that the conductive carrier is negative with respect to the electrode that is brought into contact with the dye solution placed upon the photoconductive surface.

The following examples will further illustrate the process of my invention, however, they are not to be considered as limiting my invention.

. recording material.

Example 1 A sensitized zinc oxide layer coated on aluminum foil was exposed to an image of 400 foot-candles intensity for seconds. The conductive image produced by this exposure was then developed electrolytically using a 2% solution of Malachite green dye in water and a viscose sponge brush electrode held at a potential of 80 volts positive with respect to the aluminum backing of the After electrolysis, the excess dye solution was removed from the surface with a damp sponge leaving a green dye image on the zinc oxide surface.

Example 2 A sensitized zinc oxide layer on aluminum foil was exposed in an image-wise pattern for 20 seconds using 400 foot-candles illumination. The conductive image was then developed electrolytically using a 2% solution of aniline blue dye in Water and a viscose sponge blush electrode, held at a potential of 80 volts, positive, with respect to the aluminum backing of a recording material. The excess dye solution was then removed with a damp sponge leaving a blue dye image on the zinc oxide surface.

Example 3 A sensitized zinc oxide layer on aluminum foil was exposed in an image-wise pattern for 10 seconds using 400 foot-candles illumination. The conductive image was then developed electrolytically by applying a 0.5% solu tion of Cotton blue BB (Schultz No. 1026) in water and stroking the film of dye solution on the zinc oxide layer 10 times with a brush electrode held at a potential of 10 volts, positive, with respect to the aluminum backing of the recording material. The excess dye solution was then removed with a damp sponge leaving a dye image on the zinc oxide surface.

This example was repeated as described excepting for the voltage; one strip of the image exposed recording material was developed at a potential of 30 volts, another at 60 volts, and another at 140 volts. In each instance a good useable dye image was produced by the electrolytic development.

Example 4 A fourzone cadmium sulfide/Pliolite S7 resin layer coated on Nesa glass (glass with a transparent coating of conducting stannic oxide), was simultaneously exposed and developed electrolytically using a 0.5% dye solution of Chicago Blue 63. For the exposure and development, the above-described element was held in a horizontal position with the cadmium sulfide resin layer on top. A stainless steel ring electrode was held in contact with the cadmium sulfide resin layer so that it formed a retaining wall for the dye solution which was poured over the said layer. Exposure was made through the back of the transparent conductive glass support to an image of 400 foot candle intensity for 10 seconds. During the exposure the steel electrode was held at a potential of 80 volts negative with respect to the Nesa glass support (cadmium sulfide acting as the anode). After the electrolytic development, the excess dye solution and the ring electrode were removed from the surface of the element leaving a blue dye image in the exposed areas of the cadmium sulfide resin layer.

In similar fashion other water soluble dyes having an electric charge on the dye ion when in solution may be used according to my process to produce dye images. Normally, the color of the image produced is of the same or nearly the same color as the solution of the dye when viewed by reflected light. However, I have found that a magenta dye image is produced by electrolytic deposition of Cotton blue BB (Baumwollblau BB) instead of the expected blue colored image. It is believed that the change in color in this instance is due to an unusual change in the resonance of the dye molecule. It is known that the dye is not destroyed upon electro-deposition because when it is moistened with water and a sheet of absorbent paper is pressed against the image and then removed, a blue colored dye image corresponding to the magenta image is found on the paper.

My electrolytic development process is a novel method for developing light exposed photoconductive surfaces of photoconductographic materials. It is a valuable process for producing dye images in any of the available photoconductographic materials.

I claim:

1. The method for forming a colored organic dye image by the electrolytic deposition of electrically charged, colored organic dye ions from an aqueous solution of said dye ions onto the surface of the light-image exposed light-sensitive photoconductive layer of a photoconductographic element, said layer prior to electrolytic deposition containing no incorporated dye for image formation and containing no incorporated dye precursor for image formation, said element comprising said photoconductive layer coated over a conductive layer, said method comprising the steps:

(1) electrolytically developing the exposed image on the said photoconductive layer by applying to it a Water solution of charged, colored organic dye ions, said dye being selected from the class consisting of water-soluble and water-alcohol-soluble dyes having a net electrical charge on the dye ion, and then applying to the said solution on the said layer an electrode held at an electrical potential in the range of from about 5 to about volts with respect to the said conductive layer such that the conductive layer has an electrical charge that is opposite in polarity to the net electrical charge on the said dye ions, and such that the said potential is maintained until a dye image is formed by electrolytic deposition of the said dye ions directly on the surface areas of said photoconductive layer that had been made conductive by exposure to light and then the said electrical potential is reduced to zero, and

(2) removing said solution of dye ions from the developed photoconductographic element, leaving a colored dye image on the surface areas of the photoconductive layer that had been exposed to light and substantially no dye on the surface areas of said layer that had not been exposed to light, said colored dye image having the color of the said dye ions.

2. The method for forming a colored organic dye image by the cathodic deposition of positively charged, colored, organic dye ions from an aqueous solution of said dye ions onto the surface of the light-image exposed lightsensitive photoconductive layer of a photoconductographic element, said layer prior to electrolytic deposition containing no incorporated dye for image formation and containing no incorporated dye precursor for image formation, said element comprising said photoconductive layer coated over a conductive layer, said method comprising the steps:

(1) electrolytically developing the exposed image on the said photoconductive layer by applying to it a water solution of colored organic dye ions, said dye being selected from the class consisting of watersoluble and water-alcohol-soluble triphenylmethane dyes, azine dyes, thiazine dyes and oxazine dyes, and then applying to the said solution on the said layer, an electrode held at an electrical potential in the range of from about 5 to about 150 volts with respect to the said conductive layer such that the conductive layer is the cathode and such that the said potential is maintained until a dye image is formed by cathodic deposition of the said dye ions on the surface areas of said photoconductive layer that had been made conductive by exposure to light and then the said electrical potential is reduced to zero, and

(2) removing said solution of dye ions from the developed photoconductographic element, leaving a colored dye image on the surface areas of the photoconductive layer that had been exposed to light and substantially no dye on the surface areas of said layer that had not been exposed to light.

3. The process of claim 2 in which Malachite green is the dye cathodically deposited from an ionic solution onto the said light-image exposed photoconductive layer.

4. The process of claim 2 in which Aniline blue is the dye cathodically deposited from an ionic solution onto the said light-image exposed photoconductive layer.

5. The process of claim 2 in which Cotton blue BB is the dye cathodically deposited from an ionic solution onto the said light-image exposed photoconductive layer.

6. The process of claim 2 in Which Methylene blue is the dye cathodically deposited from an ionic solution onto the said light-image exposed photoconductive layer.

7. The process of claim 2 in which Neutral red is the dye cathodically deposited from an ionic solution onto the said light-image exposed photoconductive layer.

8. The method of claim 1 for forming a colored organic dye image by the anodic deposition of negatively charged,

colored dye ions on the surface of an image exposed photoconductive layer containing cadmium sulfide.

9. The method of claim 1 for forming a colored organic dye image by the anodic deposition of negatively charged, colored dye ions on the surface of an image exposed photoconductive layer containing cadmium sultide said dye ions being selected from the class consisting of a bisazocarboxylate dye, a bisazosulfonate dye, and a bisazodisulfonate dye.

10. The method of claim 1 for forming a dye image by anodic deposition of negatively charged Chicago Blue 613 ions on the surface of an image exposed photoconductive layer containing cadmium sulfide.

References Cited by the Examiner UNITED STATES PATENTS 11/1961 Johnsonetal 204-18 3/1964 Neher 204-18 

1. THE METHOD FOR FORMING A COLORED ORGANIC DYE IMAGE BY THE ELECTROLYTIC DEPOSITION OF ELECTRICALLY CHARGED, COLORED ORGANIC CYE IONS FROM AN AQUEOUS SOLUTION OF SAID DYE IONS ONTO THE SURFACE OF THE LIGHT-IMAGE EXPOSED LIGHT-SENSITIVE PHOTOCONDUCTIVE LAYER OF A PHOTOCONDUCTOGRAPHIC ELEMENT, SAID LAYER PRIOR TO ELECTROLYTIC DEPOSITION CONTAINING NO INCORPORATED DYE FOR IMAGE FORMATION AND CONTAINING NO INCORPORATED DYE PRECURSOR FOR IMAGE FORMATION, SAID ELEMENT COMPRISING SAID PHOTOCONDUCTIVE LAYER COATED OVER A CONDUCTIVE LAYER, SAID METHOD COMPRISING THE STEPS: (1) ELECTROLYTICALLY DEVELOPING THE EXPOSED IMAGE ON THE SAID PHOTOCONDUCTIVE LAYER BY APPLYING TO IT A WATER SOLUTION OF CHARGED, COLORED ORGANIC DYE IONS, SAID DYE BEING SELECTED FROM THE CLASS CONSISTING OF WATER-SOLUBLE AND WATER-ALCOHOL-SOLUBLE DYES HAVING A NET ELECTRICAL CHARGE ON THE DYE ION, AND THEN APPLYING TO THE SAID SOLUTION ON THE SAID LAYER AN ELECTRODE HELD AT AN ELECTRICAL POTENTIAL IN THE RANGE OF FROM ABOUT 5 TO ABOUT 150 VOLTS WITH RESPECT TO THE SAID CONDUCTIVE LAYER SUCH THAT THE CONDUCTIVE LAYER HAS AN ELECTRICAL CHARGE THAT IS OPPOSITE IN POLARITY TO THE NET ELECTRICAL CHARGE ON THE SAID DYE IONS, AND SUCH THAT THE SAID POTENTIAL IS MAINTAINED UNTIL A DYE IMAGE IS FORMED BY ELECTROLYTIC DEPOSITION OF THE SAID DYE IS FORMED BY ELECTROLYTIC DEPOSITION OF THE SAID DYE IONS DIRECTLY ON THE SURFACE AREAS OF SAID PHOTOCONDUCTIVE LAYER THAT HAD BEEN MADE CONDUCTIVE BY EXPOSURE TO LIGHT AND THEN THE SAID ELECTRICAL POTENTIAL IS REDUCED TO ZERO, AND (2) REMOVING SAID SOLUTION OF DYE IONS FROM THE DEVELOPED PHOTOCONDUCTOGRAPHIC ELEMENT, LEAVING A COLORED DYE IMAGE ON THE SURFACE AREAS OF THE PHOTOCONDUCTIVE LAYER THAT HAD BEEN EXPOSED TO LIGHT AND SUBSTANTIALLY NO DYE ON THE SURFACE AREAS OF SAID LAYER THAT HAD NOT BEEN EXPOSED TO LIGHT, SAID COLORED DYE IMAGE HAVING THE COLOR OF THE SAID DYE IONS. 